how to install quartus on linux

Iam using ubuntu 10.04,now i wants to install quartus 11.1.spl_216_quartus_free_linus.sh

I went through some forums , i came to know i have to install Quartus with altera_installer for linux.

how and where to download the altera_installer.external.sh.

am very new to this , plz tel mi the step by step procedure.

how to install quartus on linux?

Thanks in Advance.